Genética de populações segregantes de feijão-caupi quanto a fixação biológica de nitrogênio

Abstract

Biological nitrogen fixation (BNF) in cowpea has shown great potential for increasing the contribution to plant nutrition, being recognized as effective in reducing the cost of production and dependence on external inputs. Segregating generations of cowpea are as efficient for FBN as their parents, but there are no reports in the literature on estimates of heritability of this character in these generations. The objective of this work was to analyze segregating parents and generations of this culture, through genetic parameters, correlations and path analysis, regarding the variables related to BNF. The experiment was carried from march to april 2016, in outdoor benches at the Experimental Sugarcane Station of Carpina (Federal Rural University of Pernambuco), located at the Zona da Mata region of the State of the Pernambuco, Northeast of Brazil, located at 7° 51' 04" south latitude, 35° 14' 27'' west longitude, and 178 m altitude, with a randomized block design and four replications. A mixture of two strains of Bradyrhizobium, recommended for cowpea, was used. The seeds were planted in polyethylene bags of 20 cm x 30 cm, using as a substrate the mixture of vermiculite washed sand in a 1:1 ratio. The parents and the generations F2, F3 and F4 were used as treatments. The plots were composed of 24 plants of each of the parents and 76 plants of each of the generations, totaling 1104 plants. The number of nodules per plant (NN), nodules dry mass (NDM), roots dry mass (RDM), shoot dry mass (SDM), nitrogen accumulated in the shoots (NAS) and nodulation efficiency were evaluated (NODE). Plant collection was performed 45 days after emergence (DAE) and the results showed that NBF in the segregating generations was as efficient as in the parents, allowing more promising genotypes to be obtained at each generation advancement. The Jinks and Pooni methodology is a viable alternative in predicting the potential of segregating populations in more advanced generations of cowpea. The phenotypic correlations between the variables showed a great influence of each of them under the others. The path analysis was adequate to explain the relationships between primary components and NAS of the plant, considering the high estimation of the coefficient of determination (R2) and the low residual effect. The direct and indirect effects of the primary variables indicated that it is possible to select plants with higher NAS content when they present higher values of the explanatory variables.